Subtle magnesium liberation of self-fabricated functional filler actuates highly efficient phosphorus removal from source-separated urine by SBBR.

Domestic wastewater source-separated treatment has attracted wide attention due to the efficiency improvement of sewage treatment systems, energy saving, resource reuse, and the construction and operation cost saving of pipeline networks. Nonetheless, the excess source-separated urine still demands further harmless treatment. Sequencing batch biofilm reactor (SBBR), a new type of composite biofilm reactor developed by filling different fillers into the sequential batch reactor (SBR) reactor, has higher pollutant removal performance and simpler operation and maintenance. However, the phosphorus removal ability of the SBBR filling with conventional fillers is still limited and needs further improvement. In this study, we developed two new fillers, the self-fabricated filler A and B (SFA/SFB), and compared their source-separated urine treatment performance. Long-term treatment experimental results demonstrated that the SBBR systems with different fillers had good removal performance on the COD and TN in the influent, and the removal rate increased with the increasing HRT. However, only the SBBR system with the SFA showed excellent PO43--P and TP removal performance, with the removal rates being 83.7 ± 11.9% and 77.3 ± 13.7% when the HRT was 1 d. Microbial community analysis results indicated that no special bacteria with strong phosphorus removal ability were present on the surface of the SFA. Adsorption experimental results suggested that the SFA had better adsorption performance for phosphorus than the SFB, but it could not always have stronger phosphorus adsorption and removal performance during long-term operation due to the adsorption saturation. Through a series of characterizations such as SEM, XRD, and BET, it was found that the SFA had a looser structure due to the use of different binder and production processes, and the magnesium in the SFA gradually released and reacted with PO43- and NH4+ in the source-separated urine to form dittmarite and struvite, thus achieving efficient phosphorus removal. This study provides a feasible manner for the efficient treatment of source-separated urine using the SBBR system with self-fabricated fillers.

Biotoxicity attenuation and the underlying physicochemical mechanism of biochar aged under simulated natural environmental conditions.

Biochar (BC), with the benefits of enhancing soil fertility, absorbing heavy metals, carbon sequestration, and mitigating the greenhouse effect, has been extensively used for soil remediation. However, the long-term changes in the biotoxicity of BC under complex environmental conditions, which are the key factors influencing the sustainable application of BC in soil, are still unclear. Herein, the biotoxicity of BC aged with various processes, including dry‒wet cycle (DW) aging, freeze‒thaw cycle (FT) aging, ultraviolet irradiation (UV) aging, and low molecular weight organic acid (OA) aging, was systematically investigated by Escherichia coli (E. coli) culture experiments. The toxicity attenuation rate (%·week-1) was proposed to more concisely and clearly compare the influence of different aging methods on BC toxicity. The results indicated that after 5 weeks of aging, the toxicity attenuation rate during the four aging modes followed the order OA aging > FT aging > UV aging > DW aging. BC was nontoxic after 1 week of OA aging, 4 weeks of FT aging, 7 weeks of UV aging, and 14 weeks of DW aging. Spectroscopic characterizations revealed that humic acids in the dissolved organic matter of BC were the main reason for the biotoxicity. In addition, the attenuation of environmentally persistent free radicals on BC during aging was also an important factor for reducing environmental toxicity. This work provides insight into the detoxification mechanism of the BC aging process under ordinary environmental conditions and guidance for the safe application of BC in soil.

Effects of regular zooplankton supplement on the bacterial communities and process performance of biofilm for wastewater treatment.

Biofilm processing technologies were widely used for wastewater treatment due to its advantages of low cost and easy management. However, the aging biofilms inevitably decrease the purification efficiency and increase the sludge production, which limited the widely application of biofilms technologies in rural area. In this study, we proposed a novel strategy by introducing high-trophic organisms to prey on low-trophic organisms, and reduce the aged biofilms and enhance treatment efficiencies in rural wastewater treatment. The effect of three typical zooplankton (Paramecium, Daphnia, and Rotifer) supplement on the purification efficiency and biofilm properties in the contact oxidation process were investigated, and the reaction conditions were optimized by an orthogonal experiment. Under optimal conditions, the biofilms weight decreased 67.6%, the oxygen consumption rate of biofilms increased 9.4%, and wastewater treatment efficiency was obviously increased after zooplankton supplement. Microbial sequencing results demonstrated that the zooplankton optimize the contact oxidation process by altering the bacterial genera mainly Diaphorobacter, Thermomonas, Alicycliphilus and Comamonas. This research provides insight into mechanism of the zooplankton supplement in biological contact oxidation process and provides a feasible strategy for improving the rural sewage treatment technology.

Identification of microbial consortia for sustainable disposal of constructed wetland reed litter wastes.

Reed is a typical emerged plant in constructed wetlands (CWs). Its litters were used as raw materials for preparing Fe-C ceramic-filler (Fe-C-CF). The physical and chemical properties of Fe-C-CF were studied under different conditions, including the mass ration of Fe to carbon (Fe/C ratio), sintering temperature, and time, to determine the optimum preparing conditions. Meanwhile, the denitrification performance and CO2 emission flux of the surface flow constructed wetland (SFCW) systems were investigated when using Fe-C-CF as the matrix. The optimum preparing conditions for Fe-C-CF were Fe/C ratio of 1:1, sintering temperature and time of 500 °C and 20 min, respectively. The SFCW system with Fe-C-CF obtained a higher total nitrogen (TN), nitrate nitrogen (NO3--N), and ammonia nitrogen (NH3-N) removal efficiencies than the control SFCW system without Fe-C-CF. Compared with the heterotrophic denitrification process, the SFCW system with Fe-C-CF decreased CO2 emission by 67.9 g m-2 per year. The results of microbial community analysis indicated that addition of Fe-C-CF increased the diversity and abundance of microbial communities in the SFCW systems. The dominant genus of the SFCW system with Fe-C-CF was Bacillus, while Uliginosibacterium was the dominant genus in the system without the filler.

A comprehensive review on mixotrophic denitrification processes for biological nitrogen removal.

Biological denitrification is the most widely used method for nitrogen removal in water treatment. Compared with heterotrophic and autotrophic denitrification, mixotrophic denitrification is later studied and used. Because mixotrophic denitrification can overcome some shortcomings of heterotrophic and autotrophic denitrification, such as a high carbon source demand for heterotrophic denitrification and a long start-up time for autotrophic denitrification. It has attracted extensive attention of researchers and is increasingly used in biological nitrogen removal processes. However, so far, a comprehensive review is lacking. This paper aims to review the current research status of mixotrophic denitrification and provide guidance for future research in this field. It is shown that mixotrophic denitrification processes can be divided into three main kinds based on different kinds of electron donors, mainly including sulfur-, hydrogen-, and iron-based reducing substances. Among them, sulfur-based mixotrophic denitrification is the most widely studied. The most concerned influencing factors of mixotrophic denitrification processes are hydraulic retention times (HRT) and ratio of chemical oxygen demand (COD) to total inorganic nitrogen (C/N). The dominant functional bacteria of sulfur-based mixotrophic denitrification system are Thiobacillus, Azoarcus, Pseudomonas, and Thauera. At present, mixotrophic denitrification processes are mainly applied for nitrogen removal in drinking water, groundwater, and wastewater treatment. Finally, challenges and future research directions are discussed.

Simultaneous recovery of nutrients and improving the biodegradability of waste algae hydrothermal liquid.

The ever-increasing algae biomass due to eutrophication brings an enormous destruction and potential threat to the ecosystem. Hydrothermal carbonization (HTC) is a potential means converting algae to value added products such as sustainable bioenergy and biomaterials. However, the waste aqueous phase (AP) produced during the HTC of algae biomass needs to be treated carefully in case of the second pollution to environment. In this study, a model microbe (E. coli) was adopted for the microbial pretreatment of AP, by which the bioavailability of AP could be improved, and the nutrients could be reclaimed though struvite precipitation. Three-dimensional fluorescence spectra and GC-MS results illustrated that E. coli pretreatment could convert a large number of organic nitrogenous compounds to ammonia nitrogen by degrading aromatic protein substances and deaminating nitrogenous heterocyclic compounds. Afterwards, a serious of characterizations confirmed that 81.13% of ammonia nitrogen could be recovered as struvite though precipitation. Life cycle assessment indicates the cost of the two-step treatment process was much lower than that of conventional wastewater treatment processes, and is beneficial to environment. This work provides an environment-friendly strategy for the comprehensive utilization of algae, which may contribute to alleviating the algal disasters and bring certain economic benefits though algal treatment.

Investigations on the dissolved organic matter leached from oil-contaminated soils by using pyrolysis remediation method.

Pyrolysis, as a convenient and fast technology, has been proved to be promising in the remediation of oil-contaminated soil. However, little is known about the dissolved organic matter (DOM) associated with pyrolyzed oil-contaminated soil and its environmental impact. Herein, optical spectroscopic techniques (i.e., absorbance and fluorescence) were adopted to reveal the relationship between the pyrolysis temperature and the characteristics of the DOM and the associated phytotoxicity. Results show that one of the main factors determining the properties and phytotoxicity of DOM leached from the pyrolyzed soil is the critical temperature (approximately 325 °C) during pyrolysis. When the temperature was lower than 325 °C, more types and quantities of DOM, mainly fulvic acid-like substances, were desorbed from the soil with the temperature, which have little effect on wheat growth. However, when the temperature was in the range of 325-550 °C, the type and quantity of DOM increased first and then decreased as the temperature increased, during which the organic matter in the soil decomposed. The wheat growth was first inhibited and then promoted. Finally, the correlation between the spectral indices of DOM with the phytotoxicity suggested that fluorescent components identified by parallel factor analysis were positively correlated with phytotoxicity. This study indicates the pyrolytic remediation of oil-contaminated soil should avoid some critical temperature ranges.

Bio-coal: A renewable and massively producible fuel from lignocellulosic biomass.

Development of renewable energy is essential to mitigating the fossil fuel shortage and climate change issues. Here, we propose to produce a new type of energy, bio-coal, via a fast pyrolysis coupled with atmospheric distillation process. The high heating values of the as-prepared bio-coals from the representative biomass are within 25.4 to 28.2 MJ kg-1, which are comparable to that of the commercial coals. Life cycle assessment further shows that the bio-coal production process could achieve net positive energy, financial, and environmental benefits. By using available biomass wastes as feedstock, China is expected to have a total bio-coal production of 402 million tons of standard coal equivalent, which is equal to 13% of national coal consumption. It would grant China an opportunity to additionally cut 738 million tons of CO2 emission by substituting an equal amount of coal with bio-coal in 2030.

Biochar-supported magnetic noble metallic nanoparticles for the fast recovery of excessive reductant during pollutant reduction.

The catalytic reduction of diverse pollutants by noble metal catalysts in the presence of reductants is a highly effective and widely used method. However, the considerable cost of noble metal catalysts impedes the practical application of this method, and the recovery of excessive reductants has not been reported previously. In this work, we prepared inexpensive biochar-supported magnetic noble metallic nanoparticles (NPs) and efficiently recovered the excessive reductants in the form of H2. The as-synthesized biochar-supported noble metallic NPs exhibited high H2 recovery during the 4-nitrophenol reduction reaction. Results showed that the catalysts with low noble metallic content have higher H2 recovery rate than commercial Pd/C, Ag/C, and Pt/C. The catalytic mechanism of magnetic biochar-supported noble metallic NPs was demonstrated to be a "synergetic effect", where biochar and Fe3O4 acted as accelerants that enable noble metallic NPs to produce active hydrogen for the reduction reaction, and the excess active hydrogen atoms combined to form H2.